A way to measure conductivity and carrier density of thin films atop conducing substrate is to grow a test structure with the active layer of interest on top of a different, insulating substrate, thereby eliminating the short-circuit caused by the conducting substrate. This can be problematic because the lattice constant of the conducting substrate (e.g. GaSb) can be different from the lattice constant of the insulating substrate (e.g. GaAs). The strain and defect density of the test structure are different from that of the actual device. This alters the properties of the material and can make it problematic to try to deduce any useful conclusions about device improvements. Another approach, the Four-point probe method, can measure out-of-plane conductivity with a pseudo-4-point geometry, but does not measure in-plane and off-diagonal conductivity or carrier density.